GCSE Edexcel Chemistry CHEMICAL CHANGES Complete Revision Summary

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GCSE Edexcel Chemical Changes Complete Revision Summary

CHEMICAL CHANGES

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 CHEMICAL CHANGES

  • Reactivity of Metals
  • Reactivity Series
  • Extraction of Metals
  • Acids and Bases
  • Neutralization
  • Making Soluble Salts
  • Making Insoluble Salts
  • Titrations
  • Electrolysis
  • Electrolysis of molten compounds
  • Electrolysis of aqueous solutions
  • Electrolysis of Aluminium

REACTIVITY SERIES

Metal + Dilute Acids = Salt + Hydrogen Metal + Water = Metal Hydroxide + Hydrogen

DISPLACEMENT REACTION

More reactive metal will displace the less reactive metal from its salt solution. Magnesium(More reactive metal)  + Zinc sulphate (Less reactive salt )  = Magnesium sulphate (More reactive metal displaces the less reactive) + Zinc Lead + Magnesium Sulphate                =                No reaction (Less reactive metal cannot displace the more reactive metal) Banner 3

METAL EXTRACTION

MINERALS Minerals are the rocks which contains metal. ROCKS Rocks are the minerals from which metals can be extracted profitably. REDUCTION OF METAL OXIDES Since most of the metals exist in the form of oxides, they can be extracted by reducing the ore. By HYDROGEN All the metal below hydrogen can be reduced by hydrogen BY CARBON All metal below carbon can be extracted by carbon BY ELECTROLYSIS Metals that are above carbon and hydrogen will be extract by Electrolysis Banner 4

_CHEMICAL CHANGES

OXIDATION AND REDUCTION

Oxidation
  • Gain of Oxygen
  • Loss Of hydrogen
  • Loss of electrons
C + O2                  CO2 CH4 + O2                  CO2 + H2O 2Cl–                   Cl2 + 2e Reduction
  • Loss of Oxygen
  • Gain of Hydrogen
  • Gain of electrons
CuO + Zn                  Cu + ZnO H2S + Cl2                  2HCl + S Na+ + e–                   Na Copper Oxide + Hydrogen                     Copper + Water CuO + H2                  Cu + H2O Zinc Oxide + Carbon Zinc + Carbon Dioxide 2ZnO + C                  2Zn + CO2

ACIDS BASES and ALKALI

The substance which have pH less than 7. Banner 5 Strong Acids
  • They completely dissociated in water to release H+ ions
  • Hydrochloric Acid HCl
  • Sulphuric Acid H2SO4
  • Nitric Acid HNO3
  • Phosphoric Acid H3PO4
  • HCl H+ + Cl–
  • pH = 1-3
Weak Acids
  • They are partially dissociated in water to release H+ ions
  • Vinegar: Ethanoic Acid
  • Lemon: Citric Acid
  • CH3COOH CH3COO– + H+
  • pH = 5-7
The substance which have pH greater than 7.
  • Metal Oxides, Metal Hydroxides, Metal Carbonates
  • Lithium Oxide, Lithium Carbonate, Lithium Hydroxide
  • Alkali are the soluble bases. So bases that can dissolve in water.
  • Alkali metal hydoxide
  • They release hydroxide ions when dissolved in water.

INDICATORS

Acids Bases
Taste Sour Taste Bitter
Not soapy Feels soapy
have pungent small do not have a pungent smell
When ionize give hydrogen ions Give hydroxide ions
Turns blue litmus red Turns red litmus Blue
eg Hydrochloric Acid eg Sodium Hydroxide
Sulphuric Acid

NEUTRALIZATION REACTION

Acid + Base                  Salt + Water                          Metal                  Acid Hydrochloric Acid -makes chloride salt Sulphuric Acid – makes sulphate salt Nitric Acid – makes nitrate salt Eg Sodium Chloride + Water                  Sodium Hydroxide + Hydrochloric Acid NaOH + HCl                  NaCl + H2O Potassium Oxide + Sulphuric Acid                            Potassium Sulphate + Water K2O + H2SO4                   K2SO4 + H2O Magnesium Hydroxide + Nitric Acid                   Magnesium Nitrate + Water Mg(OH)2 +2HNO3                   Mg(NO3)2 +2H2O Calcium Carbonate + Sulphuric Acid              Calcium Sulphate + Carbonate + Water CaCO3 + H2SO4                          CaSO4 + H2O + CO2 REACTIONS OF ACIDS
  • Metal + Acid = Salt + Hydrogen
  • Metal Oxide + Acid = Salt + Water
  • Metal Hydroxide + Acid = Salt + Water
  • Metal Carbonate + Acid = Salt Water + CO2
2Na + 2HCl                  2NaCl +H2 Making Insoluble salts Mix two soluble acids and Bases The salt will come out as a precipitate The precipitate is then filtered and dried. The filter paper will contain an insoluble salt. To determine the exact volume of acid and base required to make the salt, titration is carried out.

Making Soluble Salts

Mix the insoluble base into the aqueous solution of the acids. Dissolve the base into the acid until no base can be dissolved. Filter the solution to remove excess undissolved base. The run off is then crystallized to remove all the water. After evaporation the crystals will collect at the size of the vessel. The crystals can then be dried.

ELECTROLYSIS

  • Electrolysis – The breaking of ionic compound by passing electricity.
  • Electrolyte – The substance that undergoes Electrolysis
  • Electrode – The two conducting rods dipped in an electrolyte
  • Cathode – Where Cations (+ve charge ions) go. So it is negatively charge electrode
  • Anions – Where anions (-ve charge ions) go. So it is positively charged.

ELECTROLYSIS OF MOLTEN IONIC COMPOUNDS

Ionic compounds conduct Electricity when in molten or in solution as the ions are free to move when they’ are in solvent or dissolved in water. Molten Sodium Chloride NaCl                   Na+(goes towards cathode) + Cl–(goes towards anode) Cathode                    Reduction Na+ + e–                  Na(s) Anode                        Oxidation 2Cl–                  Cl2(g) + 2e– O – Oxidation I – Is L – Loss R – Reduction I – Is G – Gain

ELECTROLYSIS IN SOLUTIONS

In Solution the water also gets ionized and dissociate into H+ and OH- which also competes with the ionic compounds ions to discharge. Sodium Chloride Solution Ions H+ + OH– Na+ + Cl– At Cathode 2H+ + 2e–                          H2(g) Rule – At the cathode, the element with least reacitivity will get discharged and gains electrons. For that we have to look at the reactivity series At Anode 2Cl–                  Cl2 + 2e– For Anode, the rule is – Halide> OH– > other negative ions Remaining Solution Na+ + OH– Potassium Sulphate solution Ions K+ + SO42- H+ + OH– At Cathode 2H+ + 2e–                          H2 At Anode 4OH–                  O2 + 2H2O + 4e– Remaining Solution K2SO4

ELECTROLYSIS OF ALUMINIUM OXIDE

Bauxite an ore of aluminium is used which contains aluminium in the form of aluminium oxide. Al2O3                 Al3+ O2- Bauxite is mixed with cryolite. Cryolite lowers the melting point of aluminium oxide making it melt at a lower temperature. At Anode 2O2-                  O2 + 4e– Oxygen evolved reacts with graphite electrode forming carbon dioxide. Therefore, they are used up and needs regular replacing At Cathode Al3+ + 3e–                          Al(s) O2 + C                 CO2 Baneer 6

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Chemical Changes